1. Field of the Invention
The present invention relates to a printer having a development device for developing an electrostatic latent image on a photosensitive body to create a visible image, which is used for an electrophotographic apparatus, etc., and more particularly to a printer which utilizes previously used development toner particles.
2. Description of Related Art
A conventional process unit adopting a conventional toner particle collecting method which is used for the electrophotographic apparatus will be explained with reference to FIG. 5 and FIG. 6. A process unit 30 installed on the electrophotographic apparatus main body is supported by a case 32 which is in the apparatus. This process unit 30 includes a photosensitive drum 33, a scorotron charger 34, a development device 36, and a cleaning device 38. The photosensitive drum 33 is formed by a cylinder-type conductive base substance such as aluminum on which photoconductive material is coated. The scorotron charger 34, a light scanning device 35, the development device 36, a corotron transfer device 37, and the cleaning device 38 are arranged according to the rotational direction indicated by the arrow Y in FIG. 5 around the photosensitive drum 33.
The development device 36 stores magnetic toner particles 39 and has a developing sleeve 40 which rotates in a direction indicated by the arrow X in FIG. 5, and carries the magnetic toner particles 39 to the photosensitive drum 33 when a latent image on the drum 33 is developed. A magnet roll 41 is arranged in the developing sleeve 40. The magnet roll 41 is supported to rotate around the same shaft as the developing sleeve 40 in an opposite direction indicated by the arrow V in FIG. 5. Further, the development device 36 has a trimming blade 42 which restricts the toner particles layer thickness on the developing sleeve 40. Moreover, a power supply 47 is provided for applying a voltage to the developing sleeve 40. The cleaning device 38 contains a cleaning blade 48 for removing residual toner particles on the photosensitive drum 33, an agitator 49, and a cleaning box 50 which supports the above blade 48 and the agitator 49 and stores the removed toner particles therein.
The magnetic toner particles 39 are particles whose average particle diameter is about 10 microns. Magnetic powder such as ferrite which is dispersed between 10 and 65 percentage by weight in a styrene-acrylic copolymer resin, carbon black as a coloring agent, and an acceptor such as azo dye contained metal, chlorinated paraffin, and chlorinated polyester for providing negative electrification are included therein. Moreover, various additives are adhered on the surface of the toner particles in order to shorten the time taken for the amount of charge of the toner particles to reach a predetermined value and to maintain the predetermined amount of charge. In order to adhere these additives on the surface of the negatively-charged toner particles, the electrified polarity of the additives on the toner surface is slightly charged positively and the additives on the toner surface are charged in an opposite polarity to the polarity of the magnetic toner particles 39. The following materials are used as the additives on the toner surface. For instance, inorganic corpuscles such as colloidal silica and zinc oxide; contained organic particles such as magnetic grain, polymer beads and polyvinylidene fluoride; fatty acid metal salts such as stearin acid zinc; and black pigments such as carbon black are used.
Next, the movement of the electrophotographic apparatus on which the above-mentioned process unit 30 is installed is explained. First, the surface of the photosensitive drum 33 is uniformly charged to a predetermined polarity and potential by the scorotron charger 34. The light scanning device 35 exposes the photosensitive drum 33 based on an image signal from a control device 35A, and an electrostatic latent image is formed on the photosensitive drum 33. This latent image is developed to create a visible image by the development device 36, and the visible image is transferred on a sheet 55 by the corotron transfer device 37. The image transferred on the sheet 55 is fixed with a fixing device 56 and is output from a sheet outlet (not shown). On the other hand, foreign matters such as residual toner particles adhered on the surface of the photosensitive drum 33 after transfer and paper powder from the sheet 55 are removed by the cleaning device 38, and the photosensitive drum 33 is charged again by the scorotron charger 34 and the above-described movement is repeated.
The residual toner particles on the photosensitive drum 33 are scratched with the cleaning blade 48, and fall into the cleaning box 50. The cleaning blade 48, which is formed of an excellent polyurethane rubber in the ozonization resistance and the abrasion resistance is used, and its edge is finished to uniformly contact the surface of the drum 33. Further, a free edge of the cleaning blade 48 is arranged to extend in a direction reverse to the rotating direction indicated by the arrow Y of the photosensitive drum 33, and the toner particles on the photosensitive drum 33 can be scratched and removed by applying constant pressure to the cleaning blade 48. The toner particles which fall in the cleaning box 50 are carried into an inner part of the cleaning box 50 by rotation of an agitator 49 in the direction indicated by the arrow W and are stored therein.
In the process unit thus constructed, the waste toner removed from the photosensitive drum is returned to the development device and is utilized again for using this waste toner effectively.
Construction and movement to return the waste toner in the cleaning box to the development device are explained as follows. A collecting auger 51 is provided in the cleaning box 50, and a collecting container 52 is provided on the side of the cleaning box 50. Moreover, a toner particle carrying path 53 is provided between the collecting container 52 and the development device 36, and a carrier auger 54 is provided in the toner particle carrying path 53. Each of the collecting auger 51 and the carrier auger 54 is driven by a collecting auger drive motor 51A and a carrier auger drive motor 54A, respectively. The waste toner saved in the cleaning box 50 is carried into the collecting container 52 by the collecting auger 51, and further, is returned to the development device 36 through the toner particle carrying path 53 by the carrier auger 54 for use for development again. The amount of wasted toner particles can be greatly reduced by utilizing the waste toner again as mentioned above, and it can contribute to save resources.
However, the following problems are caused in the conventional development device thus constructed. That is, when the electrostatic latent image formed on the photosensitive drum is developed to a visible image by the toner particles, the additives on the surface of the toner particles are charged to a polarity which is opposite to the polarity of the toner particles. Therefore, in general, the additives are easily transferred even if they are adhered in the non-image portion on the photosensitive body when developed, removed by the mechanical and electrical power in the developing part, and dropped and collected in the cleaning box 50. Therefore, the amount of the additives in the waste toner stored in the cleaning box 50 increases compared with the toner particles of an initial condition. Then, if development is performed using the waste toner which is not suitable for development, the additives adhere to the non-image portion on the photosensitive body. As a result, the additives adhere to the blank of the sheet and the image defect such as dirt on the sheet becomes evident, which does not happen when using new toner particles. Moreover, foreign matter such as the paper powder from sheet 55 are admixed in the waste toner. They also make the image dirty.